text:
Why don't aircraft owners put vortex generators on the top of their flaps to extend single flap lift creation past 40 degrees?
Why don't ultralight/LSA aircraft owners put vortex generators (VGs) on the top of their flaps?
I understand that the maximum flap angle for a single lift creating flap is 40°, but 80° with a double flap, if each flap is rotated at 40°.
Why not put VGs on the top of a single flap to increase its maximum lift creation angle, and thus lift, to 45°, 50° or maybe even 60°, which would allow for a slower landing speed, hopefully in the 15-20mph range?
While Vg's might have been designed for wings, they are now used for elevators as well, which is very similar to an upside down wing and flap.  See picture below. Source: Zenith

Assuming they do have significant aerodynamic benefits (I have no grounds for a reasonable opinion on that), I'd suggest that the cost and the lack of STCs is probably the primary factor.

Well, it turns out that the maximum lift for plain, and single/double/tripple slotted flap is surprisingly the same, about 40-45 deg, as shown in this post:
https://aviation.stackexchange.com/a/24652/45806
So, there would be no increased lift by adding vortex generators to deflect the flap past 40-45 deg.
The only "lift benefit" I can think of, is if the wing could generate the required lift at a lower speed, but can't due to flow separation. In this case, as shown in the bottom right diagram of the picture above, vortex generators would be of benefit.

Because the separation bubble, that vortex generators attenuate, occurs in front of the flaps.  There's no advantage to putting VGs that far back, on an ultralight or any other fixed wing aircraft.

Actually VG's are used for horizontal tails as well and are put on the elevator ( upside down flap), instead of at the front of the stabilizer ( wing portion). See pic above.

Good luck finding a wind tunnel photo or other evidence of flow separation starting that far aft, on the tailplane or on any airfoil, with or without a deflected TE control surface.  Zenith's doodle shows that VGs located there, tucked into the hinge, cause no harm when the elevator is undeflected. But it doesn't prove that, when exposed to airflow at that location, they give any benefit.

lol. Just a bad doodle. Aircraft like the Savanah come factory equipped with VG's.

Who says that the maximum flap angle is 40°? There are plenty of planes with flaps that can go beyond that. For instance, the Hawker series has flaps that can go as high as 75°.
But the thing is, having such an extreme flap angle doesn't actually increase lift. In fact, it reduces lift. That's why it's referred to as the "lift dump" setting; it's only used after touchdown, reducing lift to increase braking efficacy while also acting as an air brake.
So, to answer your question, VGs wouldn't enable flap settings over 40° because you can already do that, and even if they did, going that high wouldn't reduce the landing speed.

I understand some cubs at the Valdez STOL competition even have 90 deg flaps, to increase drag and shorten that landing roll to under 10 ft. I meant flaps for lift creation and have revised my question.

@Fred The only difference between a flap "for lift creation" and a flap to increase drag is, in fact, the angle. Here's a video of lift dump in action. You will note that the only difference between "extra lift" mode and "extra drag" mode is the angle at which the flaps meet the incoming air.

A tripple slotted flap at 45 deg  ( 15 deg each flap ), has a lot less drag  and probably infinite more lift, than a single flap at 45 deg ( which probably has no lift at 45 deg). That's my point - how to partially mimic the lift of a double or triple flap, which a single flap with no tracks or linkages.

@Fred But you didn't ask about a 45° flap. You asked about an 80° flap. If you'll watch the video I linked, you will note that the Jetstream 31 has a double-slotted flap. According to your logic, that must mean that it can increase lift up to 80° of deflection. So why didn't the pilot use that capability when they were in the air? Why didn't they fully deploy the flaps until after touchdown? Because that's not what actually happens. Increasing flaps beyond about 45° (depending on wing design) increases drag with a decrease in lift, regardless of VGs, slots, whatever.


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What is the difference between a push rod and torque tube control system?
What is the difference between a push rod and a torque tube control system for actuating control surfaces on a GA aircraft?
A push rod sounds like it could replace a cable for elevators and rudder when attached to a rudder or elevator tab.
A torque tube sounds like it has a twisting action and sounds like it could replace a bellcrank for flaps or ailerons, but really, I have no idea what the difference is.

It's not clear whether you already know what are the two solutions, and your question is what are the pros and cons of each one? or if you're asking for a description of each solution. If you don't clarify, you may have incomplete answers.

@ mins Asking for the difference between the two systems is not a asking for the pros and cons of each system.

Avoid torque tubes - at the same mass they will be much less stiff, raising the risk of flutter.

@Peter Kämpf Do you mean an embedded tube in a control surface like the tubes in the canard on a Rutan designed Varieze?

@Fred The length is the issue here. Short tubes are OK to transfer torque. If they run the length of the fuselage or wing, make them loaded in tension or compression, not torque.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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What is the meaning of a flashing white signalling light in Aldis Lamp?
In my source, I couldn't understand the flashing white description.
I translate for you; in the last row: 'çakarlı beyaz: flashing white' says that: Leave the manoeuvering area in accordance with local instructions.
My question is: What is the meaning of local 'in accordance with local instructions' Is it meant that there were some instructions before electric power was gone and the previous instructions must be followed before leaving the manoeuvering area and returning to the apron?

The signal you are talking about relates to vehicles (flashing whites can also apply to aircraft, but then it has a different meaning).
Local instructions refers to the local written rules/procedures applicable at the specific airport. In order to be allowed to drive on the maneouvering area, the vehicle driver will have undergone training and have read the local procedures. Maybe the local instructions requires the driver to leave the maneouvering area via a specific route or in a certain direction. In such cases, that would be written in the local instructions. They are called local because they are only valid at that specific airport.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Transition level has to be readback and what about transition altitude? is it also required to be readback by the pilot?
These are the readback requirements, source by https://www.skybrary.aero/index.php/Read-back_or_Hear-back
a) ATC route clearances;
b) clearances and instructions to enter, land on, take off from, hold short of, cross or backtrack on any runway; and
c) runway-in-use, altimeter settings, SSR codes, level instructions, heading and speed instructions and, whether issued by the controller or contained in Automatic Terminal Information Service (ATIS) broadcasts, transition levels.

I don't understand your question here, are you asking whether a pilot needs a clearance to go above transition level, or notify ATC when they reach transition level?

I asked that transition level has to be readback by the pilot and I wonder that transition altitude is also valid for this?

Or, is your question about having to read back altitudes stemming from not understanding the word “level” here can either mean Flight Level and/or Altitude?

That's the part that doesn't make sense @VolkanEroğlu.

I didn't want to mention flight level/altitude sir, I wanted to mention about transition level and altitude, and they are different things; if you are above the transition level and pass the transition level through below you have to set QNH however when you pass the transition altitude through above you have to set QNE. So I want to ask this; definition include the transition level but not transition altitude. What are your thoughts? @Dean F.

@GdD which part doesn't make sense, please explain it

Since the Altitude (Pressure or True) to convert from Altitude MSL to Flight Level in the US is standardized at 18,000 feet MSL, the only transition level I have heard, used or read back has been the altitude required to transit through or above an airspace. For example, ATC has cleared me to transition the DFW B, West to East, at 2000 feet MSL directly over the center of the airfield. Considering the amount and kind of traffic at the airfield, they were gracious to allow the transition. But, they were sticklers about keeping the vertical and lateral position precise.

I see sir, thanks for your explanation, I get it what you meant @DeanF.

The word “level” is used to refer to Flight Level (or Pressure Altitude). It can (and probably is in this case) also infer the word Altitude (or True Altitude). They are sometimes used interchangeably. Though, by strict definition, they are not the same.
In the US, QNH (Transition Altitude), QNE (Transition Level), and QFE (Transition Height) are not widely used much outside of the military. Instead, the term Lowest Usable Flight Level is substituted. The word “Transition” itself is commonly used to refer to passage through an area. The process to transition the Transition Layer between the Transition Altitude and the Transition Level is standardized for all flights and airspaces.
The Flight Level is the altitude standardized at an altimeter barometric pressure setting of 29.92 inches of mercury. That allows all aircraft to fly at a standardized altimeter adjustment. In theory, this should avoid confusion caused by aircraft flying at different Indicated Altitudes but the same actual True Altitude due to different Kollsman Window settings. All aircraft in the US are to adjust their altimeters and fly using Flight Levels at and above 18,000 feet MSL. Above this Flight Level, precise Absolute Altitude is not necessary.
The following was taken from the FAA-H-8083-16B, Instrument Procedures Handbook, 2017 (IPH)

So you say that although transition level and transition altitude different levels and definition include just transition level; transition altitude is also included by definition right? @Dean F.

@VolkanEroğlu - Pardon me. Would you rephrase the question, please?

Actually I get my answer above with your explanation about how it works in the US system.

@VolkanEroğlu - The pure definitions of Transition Altitude and Transition Level are listed in https://www.skybrary.aero/index.php/Transition_Altitude/Level#Fixed_Transition_Level .   In standard practice, the wording is often used nonstandardly to mean something else. Transition is commonly used as the term to mean passing through. Right or wrong, it is very common in the US. Then again, you will also hear some pilots incorrectly refer to Flight Levels below FL180.

@VolkanEroğlu - Oh, good. Glad to hear it.


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What is this biplane from an old photograph?

Copyright photo by Real Photographs No 334

Gloster Gladiator, also on YouTube.
(Answer taken from comment by mins.)

Looks like the same aircraft, G37, the prototype?

Same photo as a postcard (source).


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Why is a centrifugal compressor in aircraft engine less susceptible to stall and surge?
I have came across a similar question here. Although the answer doesn't explain much about why and is somewhat vague. I have read that centrifugal compressor can achieve a higher pressure rise per stage than axial compressor. So technically they are less susceptible to stall and surge.
How is a stall and surge occurring in a centrifugal compressor different from that occurring in axial compressor. What are the scenarios under which a centrifugal compressor stall and/or surge (Is it same as those scenarios in axial compressor. If so I do have a rough idea)? And where does stall/surge first occur in a centrifugal compressor (impeller or diffuser)?
Is it because the rotor blades of centrifugal compressors doesn't act/function like airfoils?

For a compression system operating in normal condition, a mass-flow reduction leads to an increase of pressure rise. By reducing continuously the mass-flow, you reach the point of maximum pressure ratio after which the compressor operates differently. This could bring aerodynamic stall in flow and degrade performance.

Rotating stall (often called stall) is a stable operating mechanism which allows compressor to adapt to a very small mass-flow and affects overall performance. Some stalled zones called 'cells' appear which have a very little flow (low velocity). It's possible to compare this with stall on airfoils but the blockage caused by cells will affect incidence of adjacent blades (or downstream rows). Note that stall can (quite often actually) precede surge but not always.

Surge is an instable process where the annulus average mass-flow varies with time and cyclically. The compressor pass from an un-stalled phase to a stalled one and back again. That flow instability is not only related to the compressor alone but on the whole system where it operates. It is common to modelling this with a throttle valve (see picture bellow).

In nominal operating zone, compressor is unconditionally stable since compressor and throttle lines have « opposite » behaviour. A small reduction in mass flow leads to increase the pressure rise through compressor and decrease pressure drop in throttle. Therefore, the flow will accelerate until an equilibrium.
In unstable region, the throttle do not compensate changes in pressure rise due to mass flow unsteady.

To answer your question, mechanisms presented before are valid for any compression system.
Indeed, centrifugal compressors sometimes operate with stall: near inducer tips or over the impeller due to downstream asymmetry. But they could remain stable even with stall present, and surge is less likely to occur.
The reason for this is that a large part of the compression is done by centrifugal effects with or without rotating stall. The compressor line in the stalled region (on previous diagram) is probably flatter (and so more stable) for a centrifugal.

Work done by a compressor can be estimated by Euler theorem (considering inlet/outlet moment of momentum):
This implies two ways to make work through a compressor: deviate flow (V theta) and/or enlarge section (radius r). The last one is obviously related to centrifugal forces.

If stalls occur, the deviation (V theta) will be affected, at least locally (since rotating stall is a 3D non-axisymmetric phenomena). For axial compressor, most of the pressure rise is done by deviation. This is not as significant for centrifugal compressor.

The reason comes down to the principle of operation of the compressors - a centrifugal compressor, as it's name implies, just spins around really fast, and the centrifugal force compresses the air. As you can see in the image below, the vanes of the impeller of a centrifugal compressor just help push the air around in a circle (unlike an airfoil) and centrifugal force does the compressing:
The centrifugal compressor is circled in blue. As you can see, when the impeller rotates, it pushes air to the side.

Image source - https://upload.wikimedia.org/wikipedia/commons/6/6f/Saturn_MD-120_cutaway.jpg
An axial compressor has blades that work like little rotors (which are really just rotating wings) - the rotors accelerate the air, and the stators slow the air down again, using that kinetic energy to compress the gas. Just like wings, these blades can stall and lose function whenever the input flow is disturbed enough (such that the local angle of attack of a portion of the blade is too high for the given local flow conditions). This stall can then potentially spread to other blades, or to the entire engine.
As you said, the vanes of an impeller in a centrifugal compressor don't work like airfoils (instead, they kinda just rotate and push air around, kinda like a turnstile), so if they encounter airflow disturbances, they won't stall like an airfoil would. Of course, if said airflow disturbance is something like severely restricting airflow, the compressor will surge, but this is considered rare in practice.
Therefore, it's much easier to get an axial compressor to surge or stall (just by disturbing the airflow a lot) in comparison to a centrifugal compressor, which requires airflow to be restricted.

Your answer did answer about the surge part it lacks detail about stalling. Also is it just that,centrifugal force compresses air hence it surges less?I have read from a text that the impeller can get stalled and also a rotating stall is possible in centrifugal compressor under the stable region of operation as well. Also the surging starts from diffuser passage and to minimize it the no:of vanes in diffuser is kept lesser than the no:of vanes in impeller. I did read these in textbook and these might be some points you can add.Also this is just some lines I have read, i don't know the reasons.

@AbhishekPG This might help you - https://ars.els-cdn.com/content/image/3-s2.0-B9780128098950000089-f08-71-9780128098950.jpg
Flow can still seperate from the impeller at the tip (depending on outside conditions and impeller speed), which still causes a stall. It's different from the way an airfoil in an axial compressor stalls, though, and in general, occurs much rarer.


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How pressure fields change around wing?
In the 3D case,downward turning is immediately above and below the wing is stronger than in 2D case,for the same lift.This is because more rapid dying off the pressure above and below the airfoil means the vertical pressure gradient near the wing surface is stronger than in 2D case.The airfoil pressure field dies out more rapidly ahead of the airfoil and behind,which results in less upward turning of the flow in this region.So in 3D case we have more downward turning above and below the wing and less upward turning ahead and behind.Vertical extent of pressure distribution in 3D is lower than in 2D for the same chord and lift per unit span.
Reducing vertical extent of pressure distribution means increase  pressure gradient close to the wing surface and a reduction far from the surface.
So in short, smaller vertical extent(small pressure field) of pressure=larger pressure gradient=larger force which drives downward accelaration.
Pressure gradient=delta pressure / distance (Pa/m)
Do you see some contradictory in explanation above or everything is logically?
because,when we increase AoA,vertical extent of pressure distribution is larger so pressure gradient is smaller and downward acceleration must be also smaller,but it isnt because with AoA rise downward turning(downwash) as well.
Can someone explain in detail what happend with pressure fields,pressure gradient in relation to upwash/downwash at 2D/3D wing and when change AoA...

Take a look at https://www.sciencedirect.com/topics/engineering/angle-of-attack  and  https://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/lift_formula.html.
Lift graphs have a linear portion for small angle of attacks (and in 2D scenarios), but drag and airflow (laminar (non-shedding) vs. turbulent (shedding)) are both are non-linear, and both affect pressure and thus lift, and are important in real-life and 3D calculations.

Links have a tendency to break over time.  Would you mind editing a few of the important parts of those pages into your answer?


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L/D -Bell vs Eliptical spanload?
look at this   video from 18:00-21:00 ,Al Bowers talk about benefits of bell spanload compare to classic eliptical..Can someone explain what does it mean in practice examples when design aircrafts:
1)So if we have plane with 3000kg and we must have best L/D  and if wingspan  is not constrain,then we must choose bell spanload so our new wing will be 22%longer and it will has 11% smaller induced drag?
2)Why Al Bowers  talk like airplane overall weight and wing bending moment are  same thing?If some plane have bigger wing bending moment,that dont neccesery mean that it has larger weight than plane with lower wing bending moment...
3)Why all gliders use eliptical spanload if bell spanload has better L/D?
4)What do you think,when will aircraft  industry  switch to the bell spanload solution(if ever)?

Hi, and welcome to Aviation.SE. Please summarize the content of the video you refer to; your question should stand on its own if that link rots away (or if the video is not accessible in some areas), and note that opinion-based questions (what do you think...?) are discouraged here. Also, consider taking our tour to learn how ASE works.

Ok I will delete last video and put it in new topic..

I was referring to your first video, since you do not give much of an introduction to your questions outside of "watch this".

1) So if we have plane with 3000kg and we must have best L/D and if wingspan is not constrained, then we must choose bell spanload so our new wing will be 22% longer and it will has 11% smaller induced drag?

Induced drag is not all. At high speed friction drag will dominate and at best L/D it will already contribute half of total drag. Those 22% will also add more surface  area which adds friction drag. Real designs are a compromise which looks at both components, friction and induced drag.

2) Why Al Bowers talk like airplane overall weight and wing bending moment are same thing?

He simplified things, as did Prandtl in his article which is the source of Al's wisdom. If the mass that counts (the payload) sits in the middle of the wing (i.e. in the fuselage), this simplification is justified. Airplanes need to have practical value and a big payload fraction means more practical value for the operator.

3) Why all gliders use elliptical spanload if bell spanload has better L/D?

Because they need to minimize drag with a given wing span. Given their high aspect ratio, the speed of best L/D is close to the stall speed already, so in most of the speed range friction is the dominant source of drag. By keeping wing area low, this drag contribution is kept low as well. There have even been attempts at reducing wing area in flight (fs-29, SB-11) in order to improve L/D at higher speed.

4) What do you think, when will aircraft industry switch to the bell spanload solution (if ever)?

You may not have noticed but they did move away from the elliptical lift distribution long ago. Only in the times of biplanes a constant chord over span was favored, but as soon as cantilever wings were used, wings became tapered (exceptions apply, of course). But witness the taper ratio of most wings - they would have atrocious stall characteristics if they relied on elliptical loading. Of course they use proportionally less lift near the tips in order to minimize drag.

You can see that the outer contrails of this Boeing 747's engines wrap around the contrails of the inner engines (picture source). This shows how the air is pushed down in the wake of the wing and that the centers of the vortices are slightly inboard of the outer engines. The outer wing contributes little lift; however, this is not an ideal bell-shaped distribution with download at the tips. Again, it is a compromise to minimize overall drag.

1)Do you think that AL Bower  forgot to consider frictional drag in calculations?He prove that bell spanload can reduce overall drag by 60%.          4)I think this is not examples of bell spanload,bell spanload has resultant force at wingtip tilted forward,so lift produce small thrust

@ROTOR: Without knowing Al personally, I am convinced that he considered friction drag but chose an operating point where it matters little to make the advantage of a non-elliptical distribution obvious. For 4, see the extended answer. With enough angle of attack, every wing designed with the bell-shaped distribution will create lift also on the tips.

Wing with bell spanload at wingtips allways produce lift,just lift is tilted forward from vertical axis,this cause small thrust.Strong upwash at wingtips change effective airflow..there is no download at wingtips..see picture on this link:https://aviation.stackexchange.com/questions/77662/are-we-on-the-wrong-boat-with-eliptical-spanload-all-these-years

@EBV821 Root bending is caused by the non-lift-carrying mass. The wing carries itself; it is the stuff in the middle which needs to be lifted with a force at some distance. This creates the root bending moment and causes heavy wings. Now please stop stalking me and do the rest of the thinking yourself.


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What the difference between "disengage" and "disconnect"?
The Boeing 777 uses the word "disengage" for autopilot and "disconnect" for autothrottle?
What's the difference between "disengage" and "disconnect"? Why didn't they use the same word for both of them?

Aside from some tech writer's stylistic preference or convention (and there are plenty of those out there), the practical distinction between the two words is basically nil.
There is no difference in meaning between talking about "disconnecting the autopilot" or "disengaging the autopilot", nor using either term with the autothrottles.  You will hear both terms used.
As a matter of preferring one term over the other, I hear more often to "engage" the autopilot, so "disengage" is probably the most consistent term to use when talking about turning it off. But nobody is going to be confused, or have any difference of meaning understood, by using the terms interchangeably.


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Why do the spoilers on the 737 only deploy to the flight detent after a flaps up landing?
Following an all flaps up (no flap) landing, the SPEED BRAKE
lever will not move beyond the FLIGHT DETENT and the spoilers
will not fully deploy (for reference this is stated in the Fcom 9.20.14 rev 2013).
What is the reason for this? With flap up the speed will be high and if we could use the full deflection, we can reduce the landing distance, so why restrict it?


text:
What is the relation of AIR BLEED IN message with the pack system on an Airbus A320?
Before the power-up, if the pack switches are set to the ON position and the aircraft is powered up with the APU bleed off, is there a chance that the AIR BLEED IN maintenance message comes up on Lower ECAM page?

Could you please add which aircraft you are talking about? You mention ECAM, so probably an Airbus, but which one?

A320 neo and CEO @Bianfable

On A320, if the BLEED P/B are still pushed ON, it will not be a reason from the FWC to get a an error message on the ECAM in phase 1, 2 or 10 (Elec power, 1st Eng Start and 2nd eng shutdown) But you definitely will have the FAULT in amber on the P/B itself until there is bleed from APU or Engine coming up.


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What are the flow properties for the engines of a Fokker 70 with reversers deployed?
I want to know what the approximate flow properties would be at the exit of the nozzle for a Fokker 70 with reversers deployed. What is the exit velocity of gas at the nozzle?
How do they calculate values of reverse thrust? Can anyone explain what the range of thrust settings is when using bucket reversers?

It would be noteworthy to name the engine type. The Fokker 70 uses Rolls-Royce RB.183 Tay 620-15 engines.


text:
How are aircraft brakes applied?
I read somewhere that when both rudder paddles are pushed simultaneously it produces a braking effect. Is this true?
If yes, please provide a detailed description of the above mentioned system.

Not exactly.  For normal braking, you do push on the top of both pedals, but that leaves a lot of details out.
Some aircraft have a "steerable" nose/tail wheel, which means the bottom of the rudder pedals will turn it for steering, and the top of the rudder pedals activates the brake on the respective side's main wheel.  For normal braking, you do push on the top of both pedals (with your toes).  For normal turns, you push on the bottom of one pedal (with your heel).  For tight turns, you push on both top and bottom of one pedal (with both heel and toe).
Some aircraft have a "castering" nose/tail wheel, which means it turns freely; the rudder pedals have no effect, and the only way to steer is with "differential braking" on the main wheels.  For normal braking, you do push on the top of both pedals (with your toes).  For all turns, you push on the top of one pedal (with your toe).  The heels only control the rudder.

Unless I've misunderstood something, aircraft may have "toe brake" or "heel brake" and then the above may be reversed. As a whole, pressing the whole pedal forward will turn the rudder / steer the wheel, tilting the pedal (press with toe or heel) will apply brakes.

Small planes have 2 hydraulic brakes, each operated by the rudder pedals. Press on the top of the rudder pedal, and the brake on that side activates.  My plane is 4-seater built in 1973 with 6-inch main wheels and does not have antilock/antiskid capability.  If one panics on landing and hits the brakes too early, they will lock the wheels and flat-spot the tires.
The Pilots Operating Handbook (POH) for the Cessna 177B describes them thusly:

BRAKE SYSTEM
The airplane has a single-disc, hydraulically-actuated brake on each main landing gear
  wheel. Each brake is connected, by a hydraulic line, to a master cylinder attached to
  each of the pilot’s rudder pedals. The brakes are operated by applying pressure to the
  top of either the left (pilot’s) or right (copilot’s) set of rudder pedals, which are
  interconnected. When the airplane is parked, both main wheel brakes may be set by
  utilizing the parking brake which is operated by a handle under the left side of the
  instrument panel.
For maximum brake life, keep the brake systems properly maintained, and minimize
  bake usage during taxi operations and landings.
Some of the symptoms of impending brake failure are: gradual decrease in braking
  action after brake application, noisy or dragging brakes, soft of spongy pedals, and
  excessive travel and weak braking action. If any of these symptoms appear, the brake
  system is in need of immediate attention. If, during taxi or landing roll, braking action
  decreases, let up on the pedals and hen re-apply the brakes with heavy pressure. If the
  brakes become spongy or pedal travel increases, pumping the pedals should build
  braking pressure. If one brake becomes weak or fails, use the other brake sparingly
  while using opposite rudder, as required, to offset the good brake.


text:
How to compute the airspeed change based on the Altitude change
The plot shows that: when I fly with fixed MACH, the true air speed decreases when the altitude increase; when I fly with fixed CAS, the true airspeed increases when altitude increase. So how could I compute compute how much TAS change I will get based on the altitude change when I fly with fixed MACH or CAS?

What properties of physics have you thought about and What equations have you found?

Can you please credit the image source? I am pretty sure I have seen the exact same diagramm before

At the most basic level the Mach formula is: Mach = TAS/Speed of Sound
The speed of sound is a slightly non-linear function of temperature: 38.967854*SQRT(OAT+273.15) where OAT is expressed in degrees Celsius.
So:

TAS = Mach * 38.967854*sqrt(OAT+273.15)
Mach = TAS / 38.967854*sqrt(OAT+273.15)

PART II - CAS/TAS
This is about to get real...  Mach <-> TAS is a bit easier because I’m mostly just accommodating temperature’s (OAT’s) affect on the speed of sound.  You can get there directly by entering an observed OAT at your present altitude, or you can estimate what your OAT will be at various altitudes by using a surface observation and using the standard atmosphere (ISA) lapse rate which is -0.0019812°C per foot, or -1.9812°C per thousand feet.  (Caution-For FAA written test purposes, you’re expected to use the approximation of -2°C per thousand feet.)
Converting CAS <-> TAS requires us to look at air density, which is a function of both the pressure and temperature of the air.  We’ll ignore humidity to keep things “less complicated.”  We’re either going to have to calculate rho (air density) or calculate density altitude.  We already use density altitude in GA, and it’s a less complicated formula.  So now we need:

Your pressure altitude in feet (what height above MSL your altimeter says you are, assuming the correct altimeter setting.)  We’ll call that PA.
We’ll need to use the standard temperature lapse rate that I mentioned above, which is -0.0019812°C per foot.  We don’t need to convert this to Kelvin since it’s a rate of change.  We’ll call this LR.
We need to know the ISA Standard temperature for that PA.  In physics, all temperature comparisons are done in Kelvin, so we have to express this in °K, which is °C + 273.15.  This is going to be sea level standard temperature with the lapse rate applied: 15°C – (0.0019812 * PA) +273.15.  We’ll call this STK, for Std Temp Kelvin.
We also need to convert your observed OAT from °C to °K, again by adding 273.15.  We’ll call this OATK.
Density Altitude will be:  DA = PA + (STK/LR)*(1-(STK/OATK)^0.2349690)

Only part way there.  Now we’ll take our DA and plug it into this:
TAS = CAS / ( 1 - ( .0000068755856 * DA ) )^2.127940

Or
CAS = TAS * ( 1 - ( .0000068755856 * DA ) )^2.127940

If you put the DA formula and the Kelvin conversion all into one you end up with:
TAS = CAS / ( 1 - ( .0000068755856 * (PA + (  (15-(0.0019812 * PA) + 273.15)  / 0.0019812 )*( 1-( ( 15-(0.0019812 * PA) + 273.15)/( OAT + 273.15) )^0.2349690)) ) )^2.127940

Sample problem:
PA = 10,000’; OAT = 3.5°C; CAS = 150 Kts.  Should get a TAS of 177.  I typed it up in Excel format so you should be able to paste this into Excel and it should work:
=150 / ( 1 - ( .0000068755856 * (10000 + (  (15-(0.0019812 * 10000) + 273.15)  / 0.0019812 )*( 1-( ( 15-(0.0019812 * 10000) + 273.15)/( 3.5 + 273.15) )^0.2349690)) ) )^2.127940

It turn out that TAS goes up by about 1.015x per thousand feet assuming the standard atmospheric lapse rate, accurate to less than 1Kt.

Thanks Max, from your formula, I could compute fly fix Mach, how much TAS changes based on the altitude change(due to OAT change), but how about CAS? What is CAS' relationship with TAS and OAT?

@VvV Have you seen this answer with conversion formulas?

@VvV I edited the answer and added the whole new section about CAS <-> TAS.  Let me know if you need any clarification.  After you see the math you'll realize why Dalton invented the E6B!

These formulas are near impossible to read. Please use MathJax (here is a tutorial and quick reference).

@Bianfable, I've used MathJax in the past when the question is being asked by someone who I believe has math/engineering background and is looking for an equation in general form.  For those who I believe are looking to create their own "solver" to actually play around with in order to develop their own intuition, I post them in as near an "excel pastable format" as I can.  My assumption is quite often that questions here are being asked by pilots who are "math curious," as opposed to mathematicians that are "aviation curious."


text:
Is there a difference in use of external lights for taxi in/out or takeoff/landing?
Will there be a different light pattern (like turning on/off different exterior lights) between taxi in and taxi out, and between takeoff and landing?

Do you mean aircraft lights, or runway/taxiway lighting?  And for what sort of aircraft and airport?

I mean the aircraft exterior lights

The use of beacon, strobe and navigation lights is already covered in this question: When to use beacon, anti-collision, strobe, logo, and navigation lights?

Taxi: Additionally to the navigation and beacon lights, the pilots always turn on the taxi lights during taxi. This is not only to see the taxiway in the dark, but also to signal other aircraft and ground vehicles that this aircraft is currently moving or about to start moving. The use of runway turn-off lights depends on the visibility. In the dark, they are typically turned on, but there is no need for them during daylight. The details may be airline specific as well. There is no difference between taxi out and in.
Takeoff and Landing: In general, all aircraft external lights should be turned on whenever an aircraft is on a runway. This is to increase visibility to other aircraft. There is one exception to this rule: the landing lights are typically only turned on when takeoff clearance has been received (meaning they are left off when receiving a line up and wait clearance). Again, there is no difference between the takeoff and landing roll. Some airlines use the taxi light switch as a reminder for being cleared to land during approach, but it will be on when landing.

Re landing lights always turned on, that may be true at towered or other busy airports, but not in general.

@jamesqf You might not do it, but you still should: "The FAA has a voluntary pilot safety program, Operation Lights On, to enhance the see-and-avoid concept. Pilots are encouraged to turn on their landing lights during takeoff" (quoted from this answer).


text:
What should the pilots do when fire is detected during the takeoff roll at high speed?
Let us say fire or smoke is detected during a takeoff roll when the speed is so high that the pilots can not make a full stop using the remaining runway. What is the best option: using full brake to stop even if that will cause a runway excursion or continue the takeoff and re-land?

Voting to close as there is no way to give a definite answer to this, as it obviously depends on many different variables

Before starting the takeoff, the pilots will have calculated at least 3 V speeds: V1, VR and V2. The important one for your question is V1, the takeoff decision speed. This is the critical speed that determines whether or not to reject the takeoff in case of a critical failure or other problems.
During the takeoff, there are 3 phases relevant for the decision of rejecting:

Until reaching 80 knots: At these relatively low speeds, you would reject the takeoff for any reason. Any caution message appearing or any failure you notice results in rejecting the takeoff.
Between 80 knots and V1: At these speeds, you would only reject for critical failures, like e.g. an engine failure or a fire warning.
At or after V1: At these speeds, you should never reject the takeoff unless the captain determines that the aircraft is unable to fly.

The details may depend on the exact aircraft, but here is the official list of reasons for rejecting for the Boeing 737 NG:

Prior to 80 knots, the takeoff should be rejected for any of the
following:

activation of the master caution system
system failure(s)
unusual noise or vibration
tire failure
abnormally slow acceleration
takeoff configuration warning
fire or fire warning
engine failure
predictive windshear warning
if a side window opens
if the airplane is unsafe or unable to fly.

Above 80 knots and prior to V1, the takeoff should be rejected for any
of the following:

fire or fire warning
engine failure
predictive windshear warning
if the airplane is unsafe or unable to fly.

(Boeing 737 NG QRH MAN 1.2 - Maneuvers - Non-Normal Maneuvers, emphasis mine)
As you can see, a fire or fire warning is serious enough that you want to reject up to V1. At or after V1, you should not reject for a fire warning. Rejecting a takeoff after V1 usually results in an accident, even if there is enough runway available, because the brakes may not be capable of stopping the aircraft any more:

Rejecting the takeoff after V1 is not recommended unless the captain judges the
airplane incapable of flight. Even if excess runway remains after V1, there is no
assurance that the brakes have the capacity to stop the airplane before the end of
the runway.

(Boeing 737 NG FCTM 3.23 - Takeoff and Initial Climb)

Isn't V1 based on runway length, so that by definition there isn't enough runway left to get to a stop once V1 has been reached?

@jcaron No, V1 usually comes from balanced field length, which must not be larger than available runway, but it could be much shorter. That way you have a lot of runway left, but possibly too much kinetic energy for the brakes to absorb and you might still overrun after melting your brakes.

Or to put it bluntly: if something happens after V1 that means the aircraft is unable to fly, you are screwed. You are neither able to take off nor able to stop before the end of the runway. Whatever you do, bad things are going to happen.

@JörgWMittag Yes, pretty much. The good news is that a situation where the aircraft is unable to fly is very unlikely. A dual engine failure (on a twin jet) comes to mind, but two engines will not randomly fail at the same time. Only a correlated event will cause that, like e.g. a flock of birds.

@JörgWMittag: V1 is calculated assuming engine failure. If the thrust reversers are still working, you might have more wiggle room.

@Joshua, for a fire, I wouldn't try wiggling.  Airplanes are pretty fire resistant, so the extra time needed for "take off, declare mayday, circle around and land" is less risky than gambling on an abort after V1.

@Mark Many fires proved to be really deadly really fast. And not just Concorde AF 4590.

@Bianfable thanks for your comments, V1 is only applicable for multiple-engine aircrafts, right? For single engine, is there also a V1 speed defined?

@VvV My apologies, I automatically assumed you were talking about a transport category aircraft. For single engine (or light twin) aircraft, the situation is a bit different. There is no V1 speed, so you cannot know if it still safe to reject. I would say the decision depends on the exact situation. For an engine fire in a single engine I would always reject regardless of speed. It is unlikely that the aircraft will be able to fly safely with the engine on fire, so it's better to crash at low speed after trying to stop than crashing at high speed after trying to fly.

authors: Vladimir F Героям слава


text:
What emergencies or failures should I report to ATC?
During a flight, what kinds of emergencies or failures should I report to ATC immediately? For what kind of emergencies or failures am I not required to report them?
What is the general rule? Could I have some examples?

What jurisdiction?

You don't specify a country, so I'll answer for the US and hope that other countries are similar.
14 CFR 91.183(c) is the closest I can find to a "requirement" to report an emergency.  It only directly applies to IFR flights, but I can see no reason why VFR flights shouldn't do the same.
My rule of thumb is that if I wouldn't have taken off had I known about the problem then, it needs to be reported now.  Common examples might be low fuel, rough engine, weather approaching VFR limits or required instrument failure.
Note that while the FAA earned a bad rap for excessive enforcement actions in the 1980s, in the 1990s they adopted the stance that declaring an emergency is a sign of good decision making and risk management, and the stats since then show virtually no enforcement actions after emergencies, so when in doubt, I'd err on the side of declaring.  At worst, there may be a "counseling session" if they later decide that the situation didn't warrant it.

Thanks for clarifications. Could I have examples for no need to report? For examples: If I got a flap malfunction, I can still land with a high speed, do I need to report? If I got a flight control degrade but I still have enough controllability to stay in the route and land, do I need to report? If I can not turn on the navigation lights, do I need to report?

A flap failure might result in ATC giving you a different airport or longer runway than if they didn't know.  A flight control problem makes landing dangerous, so they'd probably hold you while they roll equipment.  If nav lights aren't working, they may want to increase separation because other planes may not be able to see you.  I wouldn't have taken off with those problems, so if they happened in flight, I'd report them.

@YoungL Consider a slightly worse case scenario than an ordinary, uneventful landing. What happens if you need to go around late during final approach or even flare? (Contaminated runway, or a strong gust of wind forcing you off course.) What if what you've found out about is only part of a larger problem that might not become apparent until the wheels touch the runway? I'd probably figure that if I find myself wondering "should I say something?" then I probably should say something. That something need not be "mayday" or "emergency", it could be just "caution, navigation lights inoperative".

In an emergency, ATC have two main roles:
1) To ensure you don't hit anything (be it a mountain or another aircraft);
2) To ensure that you will be met with appropriate resources on the ground.
So if you're going to need either of those things, or in any other way can't abide by normal procedures, ATC needs to know.
So ATC need to know if you're conducting a flapless landing because you need greater separation due to your higher approach speed. They don't need to know that you're turning back because of an inoperative fuel pump below MLW - but they will likely ask you of the nature of the problem to make sure they can't do anything.


text:
Where are the fuel tank sumps on an Aquila A210?
When I drain the fuel I have to do it three times:

In addition to the drainer openings on both undersides of the wing and under the front fuselage (3 times in total).

Can you tell or show me where the third drainer (under the front fuselage) is located. Do you have a picture of it?

The third drain is at the bottom of the electric fuel pump;  The AT01 is what Aquila calls the AT210 on their web site.

Is your red arrow pointing to item #12, or to what appears to be a plug on the bottom of item #11? I'd presume the latter, but you know what happens when you ass-u-me... ;)

The fuel drain fitting is at the bottom of the electric fuel pump. #12 is just a garden variety nut.


text:
What happens if the gust alleviation system on an A380 fails?
In an answer, a user linked to this video of the gust alleviation system (GAS) on an A380. This seems like a complex system with many moving parts—all the ailerons move completely independently. What happens if the GAS fail, if for instance two ailerons get stuck in an extreme position?
Or maybe even worse: imagine a sensor failure that produces two opposite extremes on each wing, such that e.g. the left wing have all its ailerons in the up position, and the right wing ailerons in the down position.

Could this be fatal?
Are there procedures for this in some checklist?

This is a follow-up for my other question, What is a gust alleviation system?.
This is not question Why do some aircraft have multiple ailerons per wing? as far as I can possibly see (though it was marked as such).

I read somewhere the GAS works with the ailerons and the external spoilers to adjust the lift distribution all over the wing span. This is only a way to use split aileron, and if faulty, the non-faulty part may be used as traditional ailerons

Following your edit, you should enhance what part of your questions are not tackled in this answer.

You have a few questions here so I will address them independently. But first off in a more general sense you should understand that everything on an airplane is generally designed with a failure mode this helps to ensure that if something fails it fails in a way to create the least adversity to flight. However there are event scenarios where multiple units fail in such a way that an adverse condition can be encountered. Generally (if you read accident reports) these can be avoided if an emergency landing is executed earlier on.

What happens if the GAS fail, if for instance two ailerons get stuck
  in an extreme position? Or maybe even worse: imagine a sensor failure
  that produces two opposite extremes on each wing, such that e.g. the
  left wing have all its ailerons in the up position, and the right wing
  ailerons in the down position.

In this case the plane still, to an extent controllable. I don't know for the Airbus, but generally speaking all systems like this have a manual override and can be disconnected. So this is implying that the system is somehow stuck on and not responding. It should be noted that in the Airbus this system does not independently actuate the flight control surfaces and most likely is bused as input to the fly by wire system. On that note a sensor failure generally does not cause extreme inputs but instead causes no input. Most things like this are at least triple redundant (so that you can figure out which sensor is bad) and if all are providing inputs that disagree the system usually disconnects and becomes inop. So to create the case you ask about you would need to have 3 independent sensors provide the same erroneous input which is highly unlikely.

Could this be fatal?

Its hard to say, but generally speaking no, the direct failure of a single system would not be fatal.

Are there procedures for this in some checklist?

More than likely but I don't have access to the official checklists so I cant say for sure.

Flying without the GAS switched on will increase the fatigue load on the wing such that it will accumulate more stress over time. This is completely uncritical for the duration of a single flight and will only add up when the aircraft is permanently operated without the GAS working.
Basically, the GAS gives the wing a slightly longer service life. If it fails, the safe life time of the wing's structure will be shortened. Failure means that the GAS will not add its additional deflections to the control commands from the pilots or the autopilot. A failed GAS means that the control surfaces behave like those on GAS-less aircraft, i.e. no more "valse des ailerons", but no hard-over.
Now what happens when the aileron control fails is a much more severe failure case and consequently made much more unlikely by full redundancy. Every actuator, every pushrod, every control computer and every control surface is doubled such that failure of any single component will not be critical. Only a multiple failure could affect safety, but is proven to be highly unlikely.

You seem to overestimate the complexity and moving parts. The GAS is a feedback system, it has sensors that provide information to the flight computers. The flight computers can then use this to adjust the ailerons as a part of its normal flying. GAS is not a completely separate, standalone system with its own control surfaces.
Gust Alleviation System (GAS) Failure
Redundancy and good programming is key here.
By having multiple sensors, it reduces the effect of failure of one sensor and makes it easier to detect a failed sensor. If you have 3 sensors saying you have an upwards gust and the 4th saying you have a side gust your software should be capable of detecting the outlier and act accordingly.
In addition to this, the amount of adjustment the system can make is also likely to be limited to a certain value and therefore it should be incapable of asking for full aileron lock.
All of this combined makes the chance of this system being capable of causing a fatal crash highly unlikely. At best it could be a contributing factor.
System checks
As for checking the system, it is likely to be self checking. The only components directly linked to the system are the sensors and computers. If either fail the aircrafts maintenances logging system should detect it and log it or alert the pilot.
Aileron failure
This is a completely separate issue to the GAS failure.

Related: Why are critical flight computers redundant?

“This is a completely separate issue to the GAS failure.”
I was referring to the aileron that is a part of GAS.

@JonasG.Drange that would be all of them. There aren't separate ailerons for the GAS, it's the same ailerons. i.e. If to the flight controller system says it wants 5 degree deflection on port aileron and 6 degrees on starboard to maintain flight, then GAS says -1 degree for gust alleviation, the ailerons would move to 4 and 5 degree deflection accordingly. The GAS is a feedback system, not a standalone system.

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text:
Why does the NASA GL-10 Greased Lightning run on diesel?
I've been reading about NASA's experimental GL-10 Greased Lightning tilt-wing aircraft with interest.
My understanding is that this is a diesel-electric hybrid aircraft uses stored electrical energy to satisfy the much greater need for thrust during takeoff (and landing?), but for regular flying runs off fewer propellers powered by the 2x 8hp diesel engines (which presumably also are recharging the Li-Ion batteries for the next takeoff/landing) to achieve better efficiency.
The answers to this question show that diesel engines are generally poorly suited to aero applications, generally due to weight and complexity.
Why then does the GL-10 use diesel fuel instead of more common aero fuels?

Diesel is much more available world-wide than 100LL, which is currently in research to be phased out at some point in the (distant) future. 100LL is usually only available at airports, Greased Lightning is designed to operate outside of the airport environment. It would be a disadvantage to have to take a tank of 100LL or avgas for this rather than fill up at the local fuel depot.

Now that we have better materials to make diesels reasonably light, they are well suited to aero applications and the answers you link to do say that.

I know I wrote that modern, turbocharged Aerodiesels are complex, but they can be very simple if you do away with charging and electronic control. If you have ever tried to shut off a model diesel engine you know that these things are super reliable, robust and efficient.

There is a bit of a misnomer here, although the plane runs diesel engines it most likely does not run traditional diesel fuel as you would find at a gas station. Diesel engines can be run on Jet-A which is available far more widely than 100LL at airports outside the US which Ron mentions.
There are even some applications for diesel engines in GA as noted in your linked question the diamond twin star and now the Piper Archer DX have successfully been running diesel engines for some time now.
According to this paper the Cosworth AG engine was considered which the Navy has already been bench testing with JP-5 and JP-8 jet fuel. Presumably the GS motor they chose runs similarly.

The misnomer in question is calling the fuel “diesel” — a Diesel (compression-ignition) engine will happily run on about anything as long as it burns and has enough lubricating properties.

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text:
What is the reasoning behind this question about the correct altitude to avoid clear icing?
This question has been killing me for a while and it's an original PPL question:

You are approaching to an airmass with a temperature of 6 C at
10000ft. Which altitude should you be in order to avoid clear icing?
A) 14000ft
B) 12000ft
C) 6000ft
D) 9000ft

The answer is C and I have no clue why.

Are you sure it's not MINUS 6 degrees? Because +6 doesn't make a lot of sense. Mind you, -6 is also fine when there's no visible moisture around.

@Ben, +6 does make sense—the air is moving faster around the aircraft, which causes temperature to drop due to adiabatic expansion. So icing risk starts a bit higher than freezing point.

The definition for icing conditions is visible moisture at a TAT of less than 10°C. From the Boeing 737 NG FCOMv1 (SP.16.1 Supplementary Procedures - Adverse Weather):

Icing conditions exist when OAT (on the ground) or TAT (in-flight) is 10°C
or below and any of the following exist:

visible moisture (clouds, fog with visibility less than one statute
mile (1600m), rain, snow, sleet, ice crystals, and so on) is present,
or
ice, snow, slush or standing water is present on the ramps,
taxiways, or runways.

To avoid icing, you should descend to an altitude where the temperature is above 10°C. The standard lapse rate of the atmosphere according to the International Standard Atmosphere (ISA) is 2°C per 1,000 ft:

As an average, the International Civil Aviation Organization (ICAO) defines an international standard atmosphere (ISA) with a temperature lapse rate of 6.49 K/km (3.56 °F or 1.98 °C/1,000 ft) from sea level to 11 km (36,090 ft or 6.8 mi).

This would result in the following expected temperatures at the given altitudes:

A) 14,000 ft: -2°C
B) 12,000 ft: 2°C
C) 6,000 ft: 14°C
D) 9,000 ft: 8°C

This only leaves answer C) with a temperature above 10°C and therefore outside of icing conditions.
Note: The lapse rate of 2°C per 1,000 ft is only an average, the actual lapse rate could be somewhat different. Wikipedia says:

A typical value is around 5 °C/km, (9 °F/km, 2.7 °F/1,000 ft, 1.5 °C/1,000 ft).

Maybe the question assumes a lower lapse rate of 1°C per 1,000 ft, where an altitude of 6,000 ft is exactly where you would get 10°C.

Thank you for the detailed explanation. Very well explained.

An observation-- the question doesn't ask about avoiding "icing conditions" which apparently is a term that has been defined at least in relation to the aviation world as having something to do with 10 degrees C, regardless of the extreme improbability of actually encountering airframe ice at that temperature.  Rather, the question simply asks about avoiding "clear icing".

It all seems a bit dubious to me. This source linked in this answer to a related ASE question suggests that ice formation is not likely below plus 2 degrees C.  So, 9000' (corresponding to plus 8 degrees C or 46 degrees Fahrenheit in a standard atmosphere) is supposedly not an acceptable altitude to avoid clear icing?
Still, I have to wonder what could make you think that any of the other three candidate answers might possibly be better than C), 6000', corresponding to 14 degrees C (57 degrees Fahrenheit) in a standard atmosphere?
Perhaps the test question was not really designed to test your knowledge of meteorology, but rather your overall reasoning skills, as evidenced by your approach to multiple-choice questions?

Your answer contains three questions.  Perhaps better as comments?


text:
What are the benefits of long-haul airplanes servicing regional routes?
Following this answer. This is actually a set of three different questions:

How often airlines "wastes" money, by putting long-hauls (widebody aircrafts) on regional or domestic routes?
Are there any (economic?) arguments for doing so (except special cases: like no other kind of replacement for broken small plane)?
Is there any example of any regional route, that is served by long-haul on regular basis?

But, I think, that all of them can be answered with one, quite simple answer.

Like would it make sense to fly and A380 on LOG343 ?

@Antzi Yes! :->

Flightradar24 has just tweeted about Air Austral flying 144 miles (232 km) with a Boeing 777 and asking whether this would be the shortest B777-serviced route?

TL;DR You're confusing concepts, planes come in high/low capacity and range, routes come in high/low demand and long/short haul distances. A high capacity long range aircraft can operate very profitably on a short haul, high demand route... a full 747 would actually be more profitable on a 1000km route than a full 737, because although the 747 uses more fuel, it also carries a lot more passengers.

You're assuming that putting a big plane on a short route wastes money. Airlines don't work in miles per gallon like you or I do with their car... they work on income/expense. I could fly 747s on 100 mile hops all day, but if they're full of 400+ passengers each paying more than 0.25% of the running costs of that flight, I'll still make money.
If they could have used a smaller aircraft, it might waste a
little money carrying the extra weight, but you seem to be
over-simplifying things
I'm guessing this question is actually more along the lines of "How often do airliners run an aircraft that isn't completely full, and how much of that time could they have actually run a smaller aircraft?" To which the answer is "Usually, and not very often"
The economics are about running the whole system as a profit. If I have enough flights in summer that fill the aircraft, then over 12 months that bigger aircraft (highly profitable all summer, breaking even all winter) may make all money than a smaller aircraft making a small profit all winter, and a small profit all summer, but not being big enough in summer to take the entire potential demand.
Essentially, though, airlines are in the business of getting the "best fit" for their fleet. They aren't trying to get a plane in every size to have the perfect profit ratio for each flight, they are trying to get a suitable plane on each flight. This involves moving planes around as routes change etc. In an ideal world you'd run each plane exactly full of every passenger who wanted to fly on that route. In reality, we probably want a plane which is just slightly bigger than that, to cope with the small amounts of extra demand
Again you're seeing "Long haul" and "Short haul" aircraft as different concepts. They aren't. There are only high/low capacity aircraft and high/low capacity routes. Long haul routes tend to have less frequent service with larger, higher capacity aircraft (if you're travelling for 18 hours, you don't need a service with departures every 3 hours). They also tend to involve people travelling from "The UK" to "Australia" for example, so one big plane can cover all of that, and split to smaller aircraft to disperse them
Short haul routes tend to have more regular service and smaller
demand levels, partially because people are less likely to want to depart at the same time every day, and partially because they can be more fine grained - you can go from an area of one country to an area of another.
What you seem to miss is that these things are not mutually exclusive... with enough demand, larger aircraft can run short haul routes very profitably. The fact a 747 is usually profitable on long haul flights, and the fact the demand on short haul routes do not usually have enough demand for such a large aircraft, don't mean that one could never be profitable if enough people wanted to fly on it. There are airlines using 777s for example for fairly short haul journeys, very profitably, all over the world.

If you look only at fuel/seat/km, long haul aircraft are more expensive according to wikipedia: http://en.wikipedia.org/wiki/Fuel_economy_in_aircraft
But maybe it's just because they tends to carry more fuel for the long trip, and then more fuel to lift the additional weight induced by the extra fuel ?

Antzi indeed, plus all the other costs. Pilots, taxes, landing fees etc. A 400 seater wide body can carry 400 people 1000 km, cheaper than 4x 100 seater narrow bodies. Fuel is a big, but not the only, consideration

@Antzi: That page is missing significant factor. For their longer trips the long-haul aircraft have to carry more fuel at the beginning and carrying this fuel takes fuel too. So a long haul aircraft loaded for short flight will have better fuel economy than the same plane loaded for long flight. And from that comparison it can't be told by how much.

Jan, I agree but I tried to keep the focus on small vs big planes on short haul routes: it was a long post without explaining too much how a large aircraft is cheaper (per km) on a shorter route than a longer one.

The other thing to consider is that "long-haul" aircraft typically have different seating arrangements to those "short-haul" ones, primarily in business/first (which might not even exist in shorter short-haul cases!). So an airline might have a dedicated fleet of widebody aircraft for short-haul flights.

Or they can just change the seating arrangements. You wouldn't want to do it between flights, but it could easily be done between winter/summer seasons

Thank you for a great answer, that has "corrected" many of my incorrect views on this matter. I can only add, as a side, technical note, that I'm a little bit surprised, that my question brought so much attention (so many good comments and answers) and ended up with zero upvotes. I thought, that questions that brings good reception are awarded by some +1 :>

Well there's one for you, now you've pointed it out - you tend to find that questions get upvoted by people who think "Oh yes, I'd like to know the answer to that too!" rather than because it's a good, well formed question. SE users in general are much worse at upvoting questions than answers, don't worry about it

The Boeing 747SR is a short range version of what would normally be considered a long-haul aircraft.
To specifically address question 3, it regularly serves the Tokio International/Haneda (HND) to Osaka (ITM) route, which is a flight duration of roughly 1:05. JAL 123 is a well known accident on that route.

Another clear example is BA's domestic fleet of a few 767s with all-economy seating, used for LHR–EDI and LHR–GLA (both typically timetabled for 1:25).

United flies sfo-bkk-hkt and sfo-hkt-Bkk in alternation with a 747. The bangkok-Phuket let is under an hour, and there were probably only 30 people on it when I took a flight from SFO-HKT

Thank you for a great examples (all +1), that directly answers third part of my question. However I must accept the other answer, because it is more comprehensive and fixes many of my incorrect points of view to this problem.

@trejder - I agree, the other answer is much more complete.

Considering the train takes only 2h15, runs every 10min and need no reservation for that route, I wonder how do they get enough people on that plane.

@Antzi that's a great question that can probably stand on its own, but would most likely be more appropriate on Travel.SE or Business.SE or Finance.SE. That said... considering there's travel time from home to the embarkation point, if time is a concern, the flight saves you and hour and 10 minutes, and that's how they get people on the plane. (Don't know about the dollar, er... yen difference, but for business people, time is an expense, as well.)

The train from downtown Osaka to the airport takes about 1h :) in 99% of the case, the train will be faster. And I'm not even talking about potential disruptions of air traffic.

@Antzi as noted, it is a valid question. I have 3 points for you: 1) I'd imagine it's profitable for the airline in either monetary or prestige/marketing terms, 2) it's a whole new question, and 3) I believe it would be OT for Aviation.SE. It is, though, a good question.

No matter high /low capacity, airline can generate income if the plane is on the sky with sufficient passengers. That means airlines will utilise the aircrafts by maximising their operating hours.
Between long-haul flight(s) operated by large aircrafts, there may be some "gap" times, airline will operate some short-haul flight by the large aircarfts to fully utilise them.
Using China Southern as example, two of their a380s(B-6136 & B-6137) are used for short route CAN-BEK (~1100 miles) and at night they will be used for CAN-LAX (~7200 miles) and come back to Baiyun airport in the early morning of two days after (China time zone). However most of the other airlines has more complex schedules, the aircrafts used for EK857/858(DXB-KWI), the A380 shortest route(~550 miles), are used for many meduim/long-haul destinations, including MUM, JFK, HKG, LHR, SYD, BKK, FCO, BNE......
PS:Jon Story answer claimed that "long haul routes tend to have less frequent service with larger, higher capacity aircraft";however some airlines actually uses smaller aircrafts with more frequent services. Cathay have 5+ daily HKG-LHR routes (~6000miles) with b77W, exclude the night time there is approximately 3-4hrs average for each departures. Using "smaller" B777 (instead of A380) means more flexible choices for customers and the aircrafts can also be used for lower capacity long-haul routes.

I don't know if this is exactly the answer that you wanted but 5th Freedom Flights as they are called are airline and airport agreements that allow airlines to operate between two airports that aren't bases or focus cities. Examples could be Air France and KLM that operate from Jakarta and Singapore or Singapore Airlines that flies from Manchester to Munich and then onto Singapore. The only main requirement is that the flight must fly back to base. This is why usually long haul aircraft are required as the flight does fly back to the main base for the airline. Fifth freedom flights sell in either sector whether it is between the two non-base cities or between the base and another cities. This allows airlines to pick up more money and get more cash
On the other hand, long haul aircraft can be frequently used in Eastern Asia. For instance, flights from Osaka and Tokyo which is less than and hours journey can be served by 747's. The main problem with this is wear and tear this produces on the aircraft. This has caused accidents in the past due to metal fatigue and other dangers.

High-cycle service is hard on any pressurized craft...but yes: some of the air routes in the Far East are that busy :)

Yes it is a shame as it does put incredible strain on an aircraft that is meant to do only half the number of takeoffs and landings that it does in Asia. It could cause problems such as metal fatigue


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Is alpha induced angle real on 3D wing or just math concept?
Does alpha induced angle/"effective airflow" really exist in real life on 3D wing or this is just mathematical concept for calculate induced drag?
(same as lifting line theory-circulation theory is just math concept for calcualte lift ,but everyone knows that airflow dont move around wing in circle...)
Question is ,if I put AoA-sensor infront of leading edge at same position at 2D and 3D wing,will be values different or equal?
(theory tell us that angle (A) at my picture below must be less on 3D wing than 2D wing...)
(in my home made wind tunnel ,I cant see difference when I put visual AoA indicator infront of leading edge at  2D compare to  3D wing..so this is reason why I ask is this real thing(maybe angle is too small to see) or just math concept...all this mess with questions about induced drag on this forum ,starts when I do this experiments..)

here is exampels of visual AoA indicators:video 1 video 2

Congratulations for your AoA vane on the model airplane. Enjoyed watching the videos!

This is not my work I just put link of video..but yes nice to watch!

1. Summary
Induced angle of attack is technically a mathematical concept. You can't measure it directly via flow sensors [from an isolated wing]. However, it is extremely useful in understanding and predicting the production of induced drag.
Just like Newton's theory of gravity is a mathematical abstraction; but, if it helps you in understanding and predicting outcomes, you might as well accept it as real. Read the following subsections if you want to understand the potential flow aerodynamic modeling a bit better.
EDIT: provided that you have an extremely long wing (and tunnel width) to call 2D section, and provided you have a corresponding high aspect ratio wing to call 3D section, the difference in AOA measured at the same chordwise location should converge to the induced AOA.
2. Lifting-Line
Induced angle of attack comes from an aerodynamic modeling method, called Lifting Line Theory, which approximates the whole wing as one single bound vortex line that changes in vorticity strength across the span. The change in vorticity is shed via trailing vortices across the span.
Since vorticity induces cross-flow, this model predicts net downwash (downward airflow) at every point along this vortex line. And since the wing is just a line, we can neatly separate out the free-stream velocity, which may have a free-stream angle of attack, or geometric angle of attack, against the line, and a downwash velocity that modifies the flow incidence, which we can call induced angle of attack.

Image ref: https://www.researchgate.net/figure/Lifting-Line-Theory-Scheme-Epps-2010_fig1_273450664
This simplified model predicts surprisingly accurate lift for straight, mid to high aspect ratio wing, in low subsonic flight. It also predicts a new kind of drag, called induced drag, which is totally absent in 2D subsonic [potential] flow.
Now, my question is, is any wing a single vortex line? Of course not. It's a model that gives very useful engineering results. The immediate shortcoming of the model is that it doesn't predict the flow field around the wing well, at all. How can it? It's a line!
3. Lifting-Surface
We can do better by approximating the whole wing as a lifting surface (or its cousin vortex-lattice), with the whole surface producing and shedding vorticity. This model is able to predict the flow field near the wing much better, by producing a different value of downwash at every spanwise and chordwise point. In front of the wing, there will be upwash. So if you measure flow incidence in front of the wing, you will measure higher incidence than the free-stream one.

Image ref: Drela, Flight Vehicle Aerodynamics
At this point, you should realize that the induced angle of attack is no more (because there is different downwash at every chordwise point). But for the same high aspect ratio, straight tapered wing, both lifting-line and lifting surface will agree on prediction of lift and induced drag.
So once again, is a wing a flat surface of vorticity? Of course not. Wing has thickness that lifting surface doesn't handle, and nor does it predict boundary layer.

@m2as3registeredservicesohmone Thanks. But you do know that your comment here will not be heard by the guys at heli-air.net, right?

@JZYL so induced alpha angle dont exist in reality and my AoA sensor will show equal angles for 2d and 3D wing.. Your answer is opposite from m2as3registeredservices ohmone..How do you comment his answer?

@ROTOR Please read the bolded part in section 3

And I think we've already addressed this in our long winded comments last time: just because you've made the width of the tunnel same as the wing span, doesn't mean you're measuring 2D section.

My question was compare upwash angle at  2D vs 3D wing,not compare upwash angle to freestream..

@ROTOR If you have an uber long wing span, and a wind tunnel to go with it, then yes, you should measure differences. The difference should converge to induced AOA as well, provided that the 3D wing itself has high aspect ratio.

I dont understand why I need extremely long wing/tunnel width to meassure this differences?When you say extremely long ,you mean on infinity or Nasa Ames biggiest wind tunnel in the world will be enough ?

How else do you ensure you're measuring 2D without 3D effect? You can use corrections, but that's based on theory you're trying to test...

Yes I understand that,but if for example, rectangular wing is long 2m and "small" tunnel is also 2m width for 2D test(walls touch tips),and now we put this 2m wing at 30m wind tunnel for 3D test,will this be enough to meassure difference?

2m wing in 30m tunnel will definitely have less interference effects...But that's probably not what you're asking...

Yes for sure, my tunnel is only 50x50cm...

@JZYL "EDIT:provided that you have an extremely long wing (and tunnel width)" You mean infinitely long?


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Will 3D wing has smaller drag than 2D at same AoA and airflow speed?
We meassure lift and drag for 2D and 3D wing case,we use same airfoil at same AoA and same airflow speed for both case.
Wind tunnel can change test section walls width.
2D wing test:
So first we put airfoil in wind tunnel so walls touch arifoil tips(2D wing),at AoA=15degrees and airflow speed=20m/s  and meassure lift and drag..
3D wing test:
Now we increase walls width so airflow "act" like 3D wing in test section.We use same AoA=15 and same airflow speed (20m/s) over airfoil like in 2D wing- test.
note: AoA=15 is angle between chord line and freestream airflow not angle between chord line and effective airflow at 3D wing
Question is,what will be drag of 3D wing-test compare to 2D wing-test,smaller ,equal or larger?
My logic is that 3D airflow leakage on tips  will decrease overall pressure difference at wing ,so lift will be smaller than in 2D wing-test but drag will be also smaller than in 2D-test,because when you integrate smaller pressure difference over airfoil surface you will get smaller drag as well.
(BUT if we must have SAME LIFT IN BOTH TEST,than 3D wing test will have larger drag,because then we must increase AoA at 3D wing to compensate lift reduction caused by airflow leakage,so now  when we have increased AoA we also have larger drag..)
3D wing will have less drag,drag decrease when AoA decrease,3D wing "feel" effective AoA,so it fly at smaller "AoA" than 2D wing.

how blue-lift can be larger than red-lift,wing at AoA=10 can not produce larger lift than wing at AoA=20 ??

Does this answer your question? Why do wall-to-wall airfoils in wind tunnels produce no (or infinitesimal) downwash?

Summary
At relatively high Reynolds number (>1 million) and in attached flow, where the boundary layer is thin, 3D wing should always have larger overall drag than a 2D airfoil (infinite span), at the same free-stream incidence angle.
Why?
The downwash generated from trailing vortices is actually very small compared to the free-stream airspeed; therefore, the reduction in effective AOA is also very small.
This results in three effects:

Reduction in lift due to tilting. This effect is exceedingly small, since cosine of a small angle is essentially unity.
Reduction in lift and pressure drag due to lower effective AOA. The reduction in lift is small but definitely non-negligible. For unseparated flow around an airfoil, the overall pressure drag is very small to begin with, so the reduction is even smaller.
Creation of induced drag due to tilting of the lift vector. This is the main one, since sine of a small angle produces non-negligible linear factor. For example, if the local lift coefficient, $C_l$, is 0.4, and we have an effective decrease in AOA of 1.0deg, then $C_l\cos{\frac{1.0\pi}{180}}\approx 0.9998C_l\approx0.4$, while the local induced drag coefficient, $C_{d_i}$, is $C_l\sin{\frac{1.0\pi}{180}}\approx0.0175C_l=0.007$.

By the way, the drag polar you cited doesn't help your argument since it's for the whole wing (at aspect ratio of 6). What you really want to cite is the airfoil drag (from Airfoil Tools):

As you can see, the form drag (includes pressure drag) is a small portion of the overall 3D drag at aspect ratio of 6, in the linear lift range. The pressure drag increase is even smaller.
Addendum:
From your comments, it seems you have totally missed the point about induced drag. Induced drag is completely absent in 2D. In fact, if you assume that the flow is inviscid and without local supersonic flow, you have zero drag on any 2D airfoil. This is called d'Alembert's paradox.
As mentioned above, induced drag appears in 3D inviscid flow due to finite span and induced downwash.

Comments are not for extended discussion; this conversation has been moved to chat.

@Сократ, no this answer is absolutely correct. This compares a 2-D airfoil with a 3-D one, but in the linked answer we are comparing the same 3-D airfoil with and without end-plates, which makes a big difference.

@Сократ a “2D” airfoil means infinite and for rather weird reasons that can produce even infinite lift with zero (not even just finite) induced drag. But it is a theoretical construct and that property comes out of the limits for increasing span. Endplates, no matter how big, will not make the wing behave as if it was infinite, only as if it was a little longer.

@Сократ, hm, unless it is also very close to the bottom (in ground effect), it should have non-zero induced drag. The air is still being accelerated downward, so conservation of momentum requires the induced drag, and the surface is still tilted backwards and so is the pressure force.

@Сократ The question is on 2D vs 3D. It isn't (or isn't perceived to be) about wall-to-wall anything. What you're hung up on is just red herring.

@Сократ Then read the answer. #2 and #3 have this dealt with.

It looks to me like you're assuming the wing is in a wind tunnel (airflow constrained vertically). It looks to me like that may be a source of a lot of this confusion.

3D wing has more drag as it considers vortices forming at the wing tip which creates more drag.But incase of 2D wing, the wing is assumed to be infinite wing. Aerodynamically, the effect of trailing vortices reduces the slope of the coefficient of lift vs. angle of attack curve. As a result,the coefficient of lift is higher in 2D wing than 3D wing for same AoA.


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What type of license do you need to solo a glider in the UK?
What type of license do you need to solo a glider (cross-country) in the UK?
Wikipedia states that:

There is no government-issued licence at present, but EASA regulations will require one by 2015.

This doesn't seem to have updated and I couldn't find anything on the  British Gliding Association (BGA) website.

This is on the BGA website under (unsurprisingly) Laws & Rules

There is no requirement for glider pilots to comply with EASA regulations for pilot licencing until 8 April 2020. The relevant BGA requirements and guidance continue to apply.

You can further follow links to the BGA Certificates, including a Cross Country endorsement:
https://members.gliding.co.uk/library/bga-requirements-guidance/gliding-certificate-endorsements/
In part:

The Cross-Country Endorsement can only be issued if the applicant has already qualified for a Bronze Endorsement or SPL/LAPL(S) and has the approval of theCFI.

Wow. You can do that in the UK? Just get in the glider with no license and go? That's crazy! Or am I reading that wrong?

@Jamiec and what happens in 2020?!

@Cloud Hold on let me get my time machine. Let me try that one more time being slightly less facetious; It'll probably be deferred again as they still won't have sorted out the brexit mess.

@JuanJimenez you're somewhat reading it wrong. Certification as competent is done by the BGA. Any club wont let you fly their aircraft unless you're certified. Could you go and buy yourself a glider and convince someone to tow you airborne? Possibly. The same is true of powered flight other than you dont need a third party to help you.

Oh, so there is a "licensing" arrangement but for now it is managed by the BGA. Got it. :)

It's all very unclear. How many hours do you need to get certified? What are the minimum hours for an SPL? Will an SPL be better to go for now as that will last even after the review period?

@Cloud honestly, youre right. Its a common theme of aviation regulation. Clear as mud. This is the point you go down to your nearest Gliding club and ask someone who does it every day. There is the chance you can find it (or find someone here who can find it) but theres no substitute for experience.

...saying that all the requirements are right there in the link Ive provided. You just have to, you know, read.


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Could the pilots really not trim manually to overcome MCAS, as shown in the Netflix Downfall documentary?
In the recent Netflix documentary, a claim is made that once MCAS activated, after several activations, the pilots physically could not trim the aircraft due to the speed and pitch.
Is this true? I didn't think the trim wheel required pounds of force like the yoke does.

From this answer: "Excessive airloads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming."

Are you happy for this to be closed as a duplicate of the question linked above? The question is clearly different but the answer looks to answer your question too. Or, did you want some more information not supplied by that answer? If so, can you elaborate on what, specifically, you want to know that's not covered.

The problem was they could not manually trim the a/c without performing the Boeing "offload the jack" procedure developed for the 737, which requires altitude to perform because you are forced to let the airplane dive to do the offloading (in the case of a nose down runaway).
The basic problem is, if you are holding a large displacement of the elevator surface from neutral, it induces a large additional torque force, or pitching moment, within the horizontal tail system itself, much higher than with the elevator at neutral.
This torque force is absorbed by the trim screw jack and is relatively light when the elevator is at neutral, aligned with the chord line of the stab surface. However, at very large elevator displacement, the load on the screw jack, induced by the twisting force built up within the tail assembly by the elevator displacement, is more than can be overcome with the leverage available to the manual trim wheel system.
It's like you are jacking a car with one of those little scissors jacks they come with, and normally you can turn the screw fairly easily with just the normal weight of the car, but then an elephant climbs onto your car (the up elevator input), and the extra weight loads up the jack so much you can't turn it by hand any more.
The only way to turn the screw is the make the elephant get off the car, but if the elephant climbs off, the car will tip over, so you are kind of stuck.
The Boeing crew were holding elevator prevent the plane from nosing over, but this prevented them from manually working the wheel, but to work the wheel, they would have to offload the jack (make the elephant climb off) by relieving the elevator back toward neutral, but doing so pointed them at the ground, and that was that.
Here is a Youtube video presentation of the situation, filmed in a simulator:
Mentour Pilot: Boeing 737 Unable to Trim!! Cockpit video (Full flight sim)

Reducing power so that the airspeed decreases, or not leaving power up so long that the speed increases unnecessarily, will also tend to remove the elephant. "Maintain aircraft control" is step #1, for runaway stab trim, and everything else.

John I added link to a video about the situation, replicated in a sim. Feel free to remove if you do not like your answer getting poked :)

Problem is reducing power increases the pitch down, which is instantaneous, whereas the speed reduction takes time.  And the speed reduction will require up elevator to sustain.   They were boxed in once they let the stab movement go too far.  The only way out was to let the airplane dive, not possible at a couple thousand feet AGL.  Step #1 is disable the stab as soon as you possibly can.

@Jpe61 improvements welcome!

Another shortcoming not discussed:  Because Manual Trim was impossible, they might've been able to use Electric Trim (controlled by a thumb switch on the yoke). But electric trim requires the trim cut-out switches to be ON, which would have given MCAS control over the trim again.   They needed electric trim (and even that may not have been effective, its unclear), but could not get electric trim because it was turned off by the same switch that stopped MCAS.

@abelenky IIRC problem was when they turned the electric trim on, they could only take out some of the MCAS input because the pilot trim rate is much slower than the MCAS rate, and when they stopped trimming MCAS would start driving again, so it was a case of 1 step forward, 2 steps back.  If they had just disconnected right at the start before it went so far, they might have been ok with the stab shut off with the plane trimmed to 200kt instead 300 kt or whatever.

Continuing with the car jack analogy: Many scissor jacks have a nut to raise/lower the car. You can easily turn it by hand (just like the trim override wheel) until the weight of the car is on the jack. Once there's weight on the car, you have to use a lever (conveniently packaged with each new car) on the nut. Likewise, when you're in an MCAS induced trim runaway, there's so much weight on the trim, you'd have to use a lever on the manual trim wheel, however, they're not included as standard cockpit equipment on the 737-MAX.

@JohnK I don't have time to read through the final report and write an answer right now, but I'm pretty sure they concluded that, since mcas only acted for a few seconds at a time the Lion Air FO could have easily undone each of the nose down inputs with the thumb switch as was done by the pilots on the previous flight before they hit the cutout. Unfortunately the Ethiopian pilots seemed to be following Boeing's disastrous advice of treating it like a runaway trim, thus disabling the trim switches, leaving them with only an unusable manual trim wheel.

Hi John this is probably off-topic here, but is a MAX safe now? I have read they STILL have issues since resuming service https://www.bbc.co.uk/news/business-59420570

@Cloud I would have to assess the failures in detail. But two things spring to mind. The media is generally wildly inaccurate in reporting, as anyone who reads media stories on topics in which they are expert knows, and, things on airplanes are breaking all the time, so occurrences that are relatively typical get hyped. There have been problems in the CRJ program that would make you avoid them forever if I hyped them up sufficiently, but the airplane is considered quite safe and reliable. Plus safe and reliable in transport a/c is at its worst many times safer than any other method of moving.

@TomMcW Boeing's reminder to pilots that the Runaway Stab Trim procedure existed was valid. Prior to handing over control to the FO, the LA Capt. successfully countered the runaway stab (restored pitch attitude, recovered lost altitude, maintained level flight) ~22 times, using the elevator & electric trim—reflexively—just as Boeing expected any pilot would do for an un-commanded pitch change, not knowing whether it was caused by windshear, wake turbulence or system failure. But knowing that 2 switches shut off the trim system isn't intuitive—comes from basic 737 type rating training.

@John K "wildly inaccurate" is putting it mildly. The news media, aviation blogs, pilots and aviation "experts" who were not competent to analyze & evaluate airplane design did so anyway, using common sense as a substitute for the specialized, costly, difficult and lengthy education that enables a proper understanding of aeronautical engineering. The general public (including Congress) couldn't detect that the published result was plausible nonsense and swallowed it, hook, line and sinker. That's how the 737 MAX—which had nothing wrong with its design—was grounded for 20 months.

@PeteP I do think Boeing dropped the ball. The real root prob was they piggybacked the MCAS failure onto the Stab Trim Runway part of the safety analysis fault tree, and got the FAA to accept the existing STR risk category and procedural mitigations, which let them take the AOA signal from a single channel. If they'd just taken both channels and lived with a bit higher fault rate from have two BOTH REQUIRED inputs, all this would've been avoided. Result of an AOA signal problem would've been the system going inactive, instead of haywire.

@John K  (1/2)The system didn't go haywire, it worked exactly as designed. Why is MCAS at a higher risk when the effect is far more benign than a runaway caused by any other fault? It runs on a duty cycle of 9.2 sec active, 5 sec rest, but can be interrupted as soon as it starts and any pitch changes undone and altitude recovered. The proof is in the flight data records of three flights that did exactly that. One flight countered it 22 times and could have gone for another 88. Another countered it, shut it off and landed at their destination.

@John K  (2/2) Why are we trying so desperately to use sensor redundancy to prevent an event that doesn't look even remotely hazardous from ever occurring? To pretend that there's a Boeing design deficiency that allowed a CATASTROPHIC event to occur and kill 346 people, while hiding the fact that two airlines didn't give their pilots the basic training needed for the 737 type rating and they allowed a runaway trim to become a fatal dive, which is really what killed the 346 people. Ironic, we muck up the engineering to keep someone pacified while falsely accusing Boeing of cutting corners, eh?

@PeteP. The problem was the pilots didn't get specific training on the subtleties of the system and its behaviour, and when it went off due to a bad AOA vane. it added workload that admittedly marginal crews couldn't cope with.  When you build airplanes sold everywhere, you have to design to a lower level of competence if you're wise about avoiding this sort of stuff. I used to participate in design reviews with another OEM and I can imagine the internal arguments over implementation that must've gone on within Boeing.


text:
Does the FAA issue multiple physical certificates for different aircraft categories and privileges?
If one holds a private pilot certificate in both airplanes and gliders, does the FAA issue two plastic cards that one would have to carry? What if one has commercial privileges in airplanes, but private in gliders?
What about being private in airplane, but sport in powered parachute? Some schools say that if one already has a private in airplane, then powered parachute at sport level would only be a logbook endorsement rather than a new piece of plastic. I was under the impression that logbook endorsements are generally things like the ability to fly a complex airplane, rather than being a sport level in a different category of aircraft.

I think you have two different questions here, you might want to ask the sport pilot one separately.

My Remote Pilot certifícate resulted in a different card which didn’t mention my PPL ASEL.

I have 3 plastic cards, (1) Airline Transport Pilot, (2) Flight Engineer, (3) Ground Instructor, and one old paper card for Flight Instructor that expired in 1990. Each of the cards has various ratings within the type of card.

One certificate would be issued. Your highest rating would be listed on the front and on the back any lower ratings would be outlined.
Before I had passed my rotorcraft ATP my certificate read:
Airline Transport Pilot
 Airplane Single and Multiengine Land
Commerical Privileges
  Rotorcraft-Helicopter

Only one would be issued.  However, if the pilot has many several type ratings and they all do not fit on the back of one certificate, the FAA will issue a second certificate with hte remainder of the type ratings.

My certificates, ATP MEL, Private SEL (VFR only), and Private Glider are all on one plastic card.  I think Ground Instructor certificates may be a second card, but I don't have any of those so I can't tell you for certain about that.

Yes, flight instructor certificates are different.

The FAA only issues one "airman certificate" at a time. The highest level and all category/class ratings will be listed first, and then any category/class ratings not at the same level will be listed in the Limitations section.
For your first example, you would get a Commercial Pilot Certificate with ASEL and GLI ratings, and then the GLI rating would be limited to Private privileges.
The second example is weird since every Private pilot also has Sport privileges, which don't have category/class ratings. As a Sport pilot, you just need a logbook endorsement from two different CFIs (rather than a checkride with a DPE) to fly a particular type of aircraft.

There is a separate card issued for Flight Instructor and it may have a subset of privileges of those listed on your pilot certificate.  Foe example, you may be an instrument rated pilot but not an instrument flight instructor.


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What is meant by Manual Tuning of ADF/NDB using BFO?
As NDB transmission is either N0NA1A(requires BFO to be turned on for Manual Tuning, Identification and Monitoring) or N0NA2A(BFO turned on only for Manual Tuning).
My question is what exactly is meant by Manual Tuning and how does BFO help in Manual Tuning of ADF/NDB.
Thank you
How (and when) to use the BFO button on an ADF? This post explains when to use it, But I want to understand the concept of Manual tuning and Why N0NA2A needs the BFO turned on for Manual tuning?

The Beat Frequency Oscillator is a tiny little transmitter in your ADF that is
tuned very close to the station that you want to receive (*).  It puts a "beat",
or audio note as a function of the difference between the BFO frequency and the
frequency being received.  A squeal if you will.  If the station being received
is at 380 kHz. and the BFO is tuned to 381 kHz. you will hear a 1 kHz. note, the
difference between 380 and 381.

Even if the beacon you want to hear is modulated, there is a phenomenon called
carrier enhancement that lets you hear the beat note from the BFO far before you
will hear any modulation on the beacon.  You can hear that squeal when the
station is so far down into the noise that you can just barely detect that there
is "something" there.

Manual tuning is like the old style analogue radios with a dial or rolling switch for tuning, similar to old AM/FM radios in your car, etc. Old Automatic Direction Finder (ADF) systems still have a tuning knob that does the same thing.
BFO stands for Beat Frequency Oscillator. There is a bit of electrickery going on, but basically, the ADF radio receiver processes the incoming signal and splits it in two, and just about halves one of those signal's frequencies. These two signals are then layered on top of each other so you can hear them on the headset. You then proceed to tune the radio until you minimise the pulsating sound coming from the headset.
The best analogy of how this works is how a guitarist tunes by ear by comparing two strings. When they pick two strings at the same note, if they aren't in tune there is a pulsing harmonic that doesn't sound nice. When the string is tuned properly, this pulsing goes away. Same concept is happening in your ADF radio with BFO selected.
So in summary, BFO help you tune to the exact NDB frequency using your own ear as a guide.

Wow all these years I've wondered how BFO actually worked, having come along a bit too late to have to work a coffee grinder ADF.  Is it a steady tone separate from the morse code audio?

Hi John, So while manual tuning it gives us a Steady Tone and our aim is to keep turning the knob of the BFO until the tone is nullified. This signals that the station has been tuned.